1. Field of the Invention
The present invention relates to a embodiments. More particularly, the present invention relates to a embodiments useful for micro fabricating of a thin magnetic film such as the thin film of FeNi, CoFe, FeMn, CoPt or the like.
2. Description of the Background Art
MRAM (Magnetic Random Access Memory) is an integrated magnetic memory, and in these days, MRAM has attracted attention as a memory, which is rewritable without limit, and having a packing density of components as high as DRAM and a speed performance as high as SRAM. On the other hand, a thin film magnetic head, a magnetic sensor and the like constituting a magnetoresistive device such as GMR (giant magnetoresistance) and TMR (tunneling magnetoresistance) have been developed with rapid progress.
In an etching process for a magnetic material, ion milling has been well adopted. But, when using ion milling in an etching process for a magnetic material, there has been problems. For example, one problem is a difficulty of selectivity relative to masks made of various kinds of material.
With respcet to a processed shape, when using ion milling in an etching process for a magnetic material, a profile of material to be etched has tapered tails. This is also a problem.
The before described problems are caused by the reason that ion milling is a physical spattering etching.
Therefore, the ion milling is not suitable for production of MRAM with a large capacity for which an especially micro fabrication technique is required. And, in these days, if the ion milling is used for producing a large area substrate such as the substrate having 300 mm in diameter, it is difficult to process with good uniformity and with good product yield.
Recently, instead of the ion milling which involves the before described problems, techniques having been fostered in the semiconductor industry is introduced into etching process for a magnetic material.
Among the techniques having been fostered in the semiconductor industry, RIE (Reactive Ion Etching) is expected as a technique which can be used in an etching process for a magnetic material. RIE (Reactive Ion Etching) is excellent in micro fabricating property, and can secure uniformity on a large area substrate such as the substrate having 300 mm in diameter.
However the RIE technique is used widely in the semiconductor industry, if it is used in an etching process for a magnetic material, it it difficult to process magnetic materials such as FeNi, CoFe, CoPt and the like without etching residue and deposition onto a sidewall, since the RIE is generally poor in reactivity on magnetic materials such as FeNi, CoFe, CoPt and the like.
In a case where the RIE technique is employed in etching process of the before described magnetic material, a chlorine gas (Cl2 or the like) has been adopted as an etching gas. If a chlorine gas (Cl2 or the like) is used, however, there is a problem of after-corrosion and a necessity arises for removing remaining chlorine component, attached to a surface layer of a substrate, after the etching. Furthermore, another necessity has arisen for any resistance to corrosion on an RIE apparatus itself against a chlorine gas (Cl2 or the like), which is corrosive gas.
In the current state of the RIE technique to be applied to the before described magnetic materials, an effort has been directed to establish a new reaction system with no need for an aftercorrosion treatment.
Japanese Patent Application Laid-Open (JP-A) No. 8-253881 proposed a gas mixture obtained by adding carbon monoxide (CO) gas to a nitrogen-containing compound such as gases of ammonia (NH3), amines or the like as an etching gas for a magnetic materials. This gas mixture proposed in JP-A-8-253881 is hereinafter referred to as a NH3+CO gas.
Even in the before described NH3+CO gas is used as the etching gas for the before described magnetic material, however, there has been a problem to be solved as described below.
1. It is necessary to provide any facilities for performing an exhaust treatment in an RIE apparatus, since NH3 and CO are toxic.
2. In a construction of TMR, which determines a basic performance of MRAM and a magnetoresistive device, ferromagnetic layers such as CoFe or the like, from which a pinned layer and a free layer sandwiching an insulating layer made of Al2O3 or the like are made, are ferromagnetic thin films with a small thickness in the range of from 1 to 5 nm. In a case where a NH3+CO gas is used as an etching gas, etching damage is given to the before described extremely thin ferromagnetic layers to degrade magnetic characteristic thereof. So that, it is afraid that an adverse influence would be exerted to device characteristics of MRAM and a magnetoresistive device.
In accordance with miniaturization of MRAM, a magnetoresistive device and the like, a proportion of a side surface (sidewall) of the material (FeNi, CoFe or the like) to be etched relative to all of the device in an RIE treatment has been increased. Therefore, when a NH3+CO gas is used as an etching gas for the magnetic materials, it becomes difficult to neglect the degradation of a magnetic characteristic due to etching damage on a side surface (sidewall) of the material (FeNi, CoFe or the like) to be etched.